Japan Air jet spills fuel at US airport

A JAPAN Airlines (JAL) Boeing 787 been grounded in Boston following a fuel spill, one day after a fire on board another plane of the same type.

"Japan Airlines flight 7 was leaking fuel as it was about to take off," said Matthew Brelis, a spokesman for Massport, the local airport authority. Around 150 litres of fuel spilled, according to Brelis.

Since the incident around midday on Tuesday, the spill has been stopped and the tarmac cleaned up, Brelis said.

The plane is being analysed and the reasons for the problem are not yet known, a spokesperson for JAL said.

It was the second incident involving a Boeing 787 in two days.

On Monday, a smoky fire broke out on another JAL aircraft of the same model after it landed in Boston from Japan.

Boeing on Tuesday confirmed the fire appeared to have started in a battery pack for the plane's auxiliary power unit.

The US National Transportation Safety Board (NTSB) described the fire damage to the battery as "severe" and said it is sending more investigators to examine the plane.

The NTSB also formed investigative groups to look at the plane's electrical systems as well as the fire response.

Boeing has a lot riding on the long-range 787, which promises a smoother travel experience and is 20 per cent more fuel efficient than older models.

After years of delays, Boeing has delivered 49 of the planes, with almost 800 more on order.

The fire on Monday happened on the ground at Boston Logan International Airport, soon after more than 100 passengers had disembarked.

Interest is especially high in this fire because of indications that lithium batteries - which generally have not been used on large planes before the 787 - can burn very hot, with fires that are difficult to put out.

The NTSB said it took firefighters 40 minutes to put out the fire near the back of the plane.

JAL spokeswoman Carol Anderson said the airline inspected its 787s after the fire, declining to discuss the results, but noting that no schedule changes were made as a result of the inspections.

United Airlines said it inspected its six 787s overnight, but a spokeswoman would not say what the inspections found.

The Wall Street Journal reported that the inspections found an improperly installed bundle of wires connected to the same battery that burned on the JAL plane.

Electrical problems have been the 787's nemesis.

Last month, a United Airlines 787 flying from Houston to Newark diverted to New Orleans because of an electrical problem with a power distribution panel.

Last week, United said it would delay the start of 787 flights from Houston to Lagos, Nigeria, because it wanted to "improve the reliability of the aircraft".

In November 2010, a test flight had to make an emergency landing after an in-flight electrical fire which delayed flight tests for several weeks while Boeing investigated.

Boeing said the fire on Monday appears to be unrelated to previous electrical problems on the 787.

"Nothing that we've seen in this case indicates a relationship to any previous 787 power system events," Boeing said in a prepared statement.

Those earlier problems involved power panels elsewhere in a rear bay for electrical equipment.

Boeing also said it "would be premature to discuss additional details at this stage" of the investigation, but that it has shared information about the prior events with the NTSB.

Shares of Chicago-based Boeing have fallen 4.6 per cent since the fire was reported, wiping out almost $US2.7 billion of the company's value.